US20080114494A1 - Tool grip calibration for robotic surgery - Google Patents

Abstract

Telerobotic, telesurgical, and surgical robotic devices, systems, and methods selectively calibrate end effector jaws by bringing the jaw elements into engagement with each other. Commanded torque signals may bring the end effector elements into engagement while monitoring the resulting position of a drive system, optionally using a second derivative of the torque/position relationship so as to identify an end effector engagement position. Calibration can allow the end effector engagement position to correspond to a nominal closed position of an input handle by compensating for wear on the end effector, the end effector drive system, then manipulator, the manipulator drive system, the manipulator/end effector interfacing, and manufacturing tolerances.

Description

BACKGROUND OF THE INVENTION
• The present invention is generally related to medical, telesurgical, and/or telerobotic devices, systems, and methods. In an exemplary embodiment, the invention provides structures and methods that calibrate an end effector/telerobotic manipulator combination when a new surgical robotic tool is mounted on a manipulator arm.
• Minimally invasive medical techniques are intended to reduce the amount of extraneous tissue that is damaged during diagnostic or surgical procedures, thereby reducing patient recovery time, discomfort, and deleterious side effects. While many of the surgeries performed each year in the US could potentially be performed in a minimally invasive manner, only a portion of current surgeries use these advantageous techniques due to limitations in minimally invasive surgical instruments and the additional surgical training involved in mastering them.
• Minimally invasive telesurgical systems for use in surgery have been developed to increase a surgeon's dexterity and avoid some of the limitations on traditional minimally invasive techniques. In telesurgery, the surgeon uses some form of remote control (such as a servomechanism or the like) to manipulate surgical instrument movements, rather than directly holding and moving the instruments by hand. In telesurgery systems, the surgeon can be provided with an image of the surgical site at the surgical workstation. While viewing a two or three dimensional image of the surgical site on a display, the surgeon performs the surgical procedures on the patient by manipulating master control devices, which in turn control the motion of servomechanically operated instruments. The servomechanism used for telesurgery will often accept input from two master controllers (one for each of the surgeon's hands) and may include two or more robotic arms or manipulators. Mapping of the hand movements to the image displayed from the image capture device can help the surgeon provide more direct control over movement of the surgical instruments.
• While the new telesurgical systems and devices have proven highly effective and advantageous, still further improvements would be desirable. For example, work in connection with the present invention has shown that misalignment between a robotic surgical end effector and an input device can decrease the useful life of some tools, and efforts to limit such misalignment can make tool and manipulator fabrication more difficult than may be ideal. As many surgical tools may be mounted on any particular manipulator during a single surgical procedure, and as tool changes will be performed while a procedure is under way, it is generally preferable to avoid and/or minimize any tool-swap related delays to the surgical procedure.
• For the reasons outlined above, it would be advantageous to provide improved devices, systems, and methods for robotic surgery, telesurgery, and other telerobotic applications. It would be particularly beneficial if these improved technologies enhanced the precision and alignment of sophisticated robotic systems without significantly increasing complexity or costs, ideally allowing greater tool useful life and reliability.
BRIEF SUMMARY OF THE INVENTION
• The present invention generally provides improved telerobotic, telesurgical, and surgical robotic devices, systems, and methods. The present invention may calibrate end effectors having jaws or the like formed with two separate end effector elements. The grip calibration will often be performed selectively, without calibrating some or all of the other degrees of freedom of an end effector/manipulator assembly. Selective calibration of grip actuation can be performed by bringing the jaw elements into engagement with each other, such as by clamping a microforceps closed, fully closing an electrosurgical scissor, closing the jaws of a needle grasper (with no needle or other structure disposed between the grasper elements), and the like. Robotic systems employing commanded torque signals may be calibrated by bringing the end effector elements into engagement while monitoring the resulting position of a drive system, optionally identifying a maxima or minima of a second derivative of the torque data so as to identify an end effector engagement position. Calibration may be effected so that the end effector engagement position corresponds to a nominal closed position of an input handle. Such calibration can compensate for wear on the end effector, the end effector drive system, then manipulator, the manipulator drive system, the manipulator/end effector interfacing, and manufacturing tolerances of each of the components of the end effector/manipulator assembly.
• In a first aspect, the invention provides a telesurgical system comprising an input handle having a first grip member that moves relative to a second grip member in response to a hand gripping the handle. A plurality of end effectors each have surgical jaws with a first end effector element moveable relative to a second end effector element. A manipulator transmits a signal in response to mounting an end effector on that manipulator. The mounted end effector may be one of the plurality of end effectors. A processor couples the input device to the manipulator, and is configured to calibrate the mounted end effector and manipulator in response to the signal. The processor does this by causing a calibration movement of at least one of the end effector elements so as to bring the elements into mutual engagement. The processor is configured to effect articulation of the jaws of the mounted end effector in response to the gripping of the handle per the calibration.
• Typically, an input linkage supports the handle and a robotic arm of the manipulator supports the mounted end effector. The input linkage and robotic arm may each have a plurality of degrees of freedom. The processor may effect movement of the robotic arm in response to articulation of the input linkage. The processor may be configured to effect the calibration in response to mounting of the end effector onto the robotic arm before the end effector is used in a robotic surgical procedure. The processor may not determine calibration from a calibration movement of at least one degree of freedom of the robotic arm between mounting of the end effector and the robotic procedure, so that the processor selectively calibrates articulation of the jaws. Work in connection with the present invention indicates that end effector jaw alignment may limit robotic surgical tool life, may impose stringent manufacturing tolerances, and/or may impose drive system strength criteria which are more onerous than those needed for some or all other degrees of freedom in robotic surgical tools. Hence, by selectively calibrating end effector jaw engagement, overall surgical tool life, tolerances, and/or costs can be improved. In fact, the processor may not effect a calibration movement of any degree of freedom of the robotic arm between mounting of the mounted end effector and the robotic procedure, other than articulation of the jaws. While other degrees of freedom may benefit from calibration movements along with (or instead of) end effector jaw articulator, additional calibration movements of other degrees of freedom may undesirably delay resumption of a surgical procedure interrupted by a tool swap.
• Typically, the calibration will compensate for manipulator offset, manipulator wear, manipulator manufacturing tolerances, surgical instrument offset, surgical instrument wear, surgical instrument manufacturing tolerances, manipulator/surgical tool interfacing, and/or the like. The processor may monitor movement of a drive system coupled to the end effector, and can identify a change in torque. The processor may optionally comprise a filter, and the processor may determine the change in torque by applying the filter to torque data. In the exemplary embodiment, the processor determines an end effector element initial engagement position by taking a second derivative of the torque data. As a servo control loop may calculate the commanded torque from a commanded trajectory and manipulator position data, the processor may command a trajectory and monitoring the commanded torque from the servo controller so as to determine a position of the end effector where the commanded torque changes.
• The input device may apply a feedback force to the hand at a nominal closed position of the handle. The processor may affect the calibration so that the end effector initial engagement configuration corresponds to the nominal closed position of the handle. The handle may comprise a biasing means for increasing resistance to gripping of the handle beginning at the nominal closed position. The biasing means may comprise a spring, resilient bumper, or the like.
• In some embodiments, a single-element end effector may also be couplable to the manipulator. A single-element end effector identifying signal may be transmitted by the manipulator when the single-element end effector is mounted thereon, and the processor may forego grip calibration in response to the single-element end effector signal. In an exemplary embodiment, a tool type identifier may be transmitted from a memory of a tool to the processor when a tool having the single-element end effector is mounted to the manipulator, the tool type identifier being used by the processor to look up, from a table of the processor's memory, a parameter indicating that grip calibration need not be performed.
• In the exemplary embodiment, the processor is configured to effect the calibration once per robotic procedure for each end effector mounted on the manipulator. If an end effector is mounted on a second manipulator, the processor can again effect the calibration once per robotic surgical procedure for that end effector/manipulator combination. The calibration may be stored during the procedure in a memory of the processor so that when a tool has been removed from a particular manipulator and is subsequently remounted onto that manipulator, the calibration information can be applied without causing the calibration movement and the like.
• In another aspect, the invention provides a telerobotic system comprising an input having a linkage supporting a handle. The handle has a first grip member that moves relative to a second group member when a hand grips the handle. The linkage is articulable for repositioning of the handle. A plurality of end effectors each comprise articulatable jaws with a first end effector element moveable relative to a second end effector element. manipulator having a robotic arm movably supports a mounted end effector from among the plurality of end effectors. A processor couples the input device to the manipulator. The processor determines the calibration of the mounted end effector by causing a calibration movement of the end effector elements into mutual engagement. The processor effects articulation of the jaws of the mounted end effector in response to the gripping of the handle per the calibration.
• In another aspect, the invention provides a telesurgical method comprising mounting a first surgical end effector to a manipulator. The end effector comprises jaws with a first end effector element movable relative to a second end effector element. The mounted first end effector and its supporting manipulator are calibrated by moving at least one of the end effector elements so as to bring the elements into mutual engagement. A handle is gripped with a hand so that a first grip member moves relative to a second grip member. An articulation signal is computed in response to the gripping of the handle per the calibration. The jaws articulate in response to the articulation signal so that the jaws of the first end effector move in correlation with the gripping of the handle.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIGS. 1A and 1B are perspective views illustrating a master surgeon console or workstation for inputting a surgical procedure, and a robotic patient-side cart for robotically moving surgical instruments having surgical end effectors at a surgical site, respectively.
• FIG. 2 is a side view showing an exemplary input device for use with the master control workstation ofFIG. 1A.
• FIG. 2A is a perspective view of a handle and wrist of the input device ofFIG. 2.
• FIG. 3 is a perspective view of an exemplary robotic surgical instrument or tool having a memory and a data interface.
• FIGS. 3A-3F are perspective views of a plurality of different end effectors for surgical instruments of different types.
• FIG. 4 shows a block diagram representing control steps followed by the control system of a minimally invasive surgical robotic apparatus in effecting movement of the end effector of the instrument ofFIG. 3 in response to the movement of the input device ofFIG. 2.
• FIG. 5A-5D schematically illustrate master/slave following forces applied to grip different sized objects.
• FIGS. 6A-6C are functional block diagrams schematically illustrating master/slave arrangements for manipulating the position, orientation, and jaws of a robotic surgical instrument.
• FIG. 7 schematically illustrates an exemplary master/slave robotic control system for actuating jaws of an end effector while providing tactile feedback to a hand of an operator.
• FIG. 8 is a functional block diagram schematically illustrating a telesurgical system according to the principles of the present invention.
• FIG. 9 graphically illustrates a relationship between joint position and servo counts during actuation of a surgical robotic end effector in the system ofFIG. 8.
• FIG. 10 graphically illustrates a relationship between commanded torque and servo counts during end effector actuation in the system ofFIG. 8.
• FIG. 11 graphically illustrates a relationship between commanded torque and servo counts as taken from the data ofFIG. 10, in which the commanded torque has been filtered.
• FIGS. 12A-12C graphically illustrate taking of a second derivative of the relationship illustrated inFIG. 11.
• FIG. 13 graphically illustrates a relationship between commanded torque and joint position, and identifies an initial end effector engagement configuration at which the end effector elements are brought into mutual engagement.
DETAILED DESCRIPTION OF THE INVENTION
• The present invention generally provides telerobotic, telesurgical, and surgical systems, devices, and methods. The invention is particularly advantageous for use with robotic surgical systems, in which a plurality of surgical instruments will be sequentially mounted on a manipulator during the surgical procedure. Loss of correlation between an input handle grip actuation and jaw articulation of telesurgical systems can be particularly problematic during telesurgery, and may be significantly more problematic than maintaining correlation between other input and output degrees of freedom in a surgical master/slave system. In some embodiments, by selectively calibrating end effector jaw movement (as opposed to calibrating all degrees of freedom of the slave), unnecessary surgical delays during tool swaps (in which one surgical instrument is removed from the manipulator and replaced with a different surgical instrument) can be avoided. In other embodiments, calibration of all axes may be performed.
• While the most immediate applications for the present invention may include telesurgical systems, the inventions described herein may also find applications in other telerobotic and robotic surgical systems.
• As used herein, the term “tool” encompasses robotic tools having robotic end effectors for coupling to robotic systems. The term “instrument” encompasses medical instruments, including both those having articulatable jaws (such as microforceps, needle graspers, staplers, electrosurgical scissors, and the like) and those having a single end effector element (such as scalpels, electrosurgical coagulators, and the like). In the exemplary embodiment, a robotic surgical system makes use of a series of removable and replaceable end effectors supported by a robotic arm, so that the end effector assembly is both a tool and an instrument. In robotic embodiments used in non-surgical applications, the end effector assembly may comprise a robotic tool that is not a medical instrument.
• The data, reprogrammable software, program method steps, and method steps described herein may be embodied in a machine readable code and stored as a tangible medium in a wide variety of differing configurations, including random access memory, non-volatile memory, write once memory, magnetic recording media, optical recording media, and the like. Along with software, at least some of the programming and data may be embodied in the form of hardware or firmware.
• Referring toFIG. 1A of the drawings, an operator workstation or surgeon's console of a minimally invasive telesurgical system is generally indicated byreference numeral200. Theworkstation200 includes aviewer202 where an image of a surgical site is displayed in use. A support tool4 is provided on which an operator, typically a surgeon, can rest his or her forearms while gripping two master controls (seeFIG. 2), one in each hand. The master controls or input devices are positioned in aspace206 inwardly beyond thesupport204. When using thecontrol workstation200, the surgeon typically sits in a chair in front of the control station, positions his or her eyes in front of theviewer202 and grips the master controls, one in each hand, while resting his or her forearms on thesupport204.
• InFIG. 1B of the drawings, a cart or surgical station of the telesurgical system is generally indicated byreference numeral300. In use, thecart300 is positioned close to a patient for whom surgery is planned, and the base of the cart is then maintained at a stationary position until a surgical procedure has been completed.Cart300 typically has wheels or castors to render it mobile. Theworkstation200 is typically positioned at some distance from thecart300, optionally being separated by a few feet within an operating room, althoughcart300 andworkstation200 may alternatively be separated by a significant distance.
• Thecart300 typically caries three robotic arm assemblies, although more than three arms may also be provided or may be the norm for some embodiments. One of the robotic arm assemblies, indicated byreference numeral302, is arranged to hold animage capturing device304, e.g., an endoscope, or the like. Each of the twoother arm assemblies10 includes asurgical instrument14. Theendoscope304 has aviewing end306 at a distal end of an elongate shaft.Endoscope304 has an elongate shaft to permitviewing end306 to be inserted through an entry port into an internal surgical site of a patient's body. Theendoscope304 is operatively connected to theviewer202 to display an image captured at itsviewing end306 on the viewer. Eachrobotic arm assembly10 is normally operatively connected to one of the master controls, although the processor may alter which robotic arm assembly is operatively connected with a master control. Thus, the movement of therobotic arm assemblies10 is controlled by manipulation of the master controls. Theinstruments14 of therobotic arm assemblies10 have end effectors mounted on wrist members, which are in turn pivotally mounted on distal ends of elongate shafts of theinstruments14.Instruments14 have elongate shafts to permit the end effectors to also be inserted through entry ports into the internal surgical site of a patient's body. Movement of the end effectors relative to the ends of the shafts of theinstruments14 is also controlled by the master controls.
• Therobotic arms10,302 are mounted on acarriage97 by means of setupjoint linkages95. Thecarriage97 can be adjusted selectively to vary its height relative to abase99 of thecart300, as indicated by arrows K. The setupjoint linkages95 are arranged to enable the lateral positions and orientations of thearms10,302 to be varied relative to a vertically extendingcolumn93 ofcart300. Accordingly, the positions, orientations and heights of thearms10,302 can be adjusted to facilitate passing the elongate shafts of theinstruments14 and theendoscope304 through the entry ports to desired positions relative to the surgical site. When thesurgical instruments14 andendoscope304 are so positioned, the setupjoint arms95 andcarriage97 are typically locked in position.Workstation200 andcart300 are described in more detail in U.S. Pat. No. 6,424,885, the full disclosure of which is incorporated herein by reference.
• Anexemplary input device220 andsurgical instrument14 are illustrated inFIGS. 2 and 3, respectively.Input device220 includes anarm222 and awrist224 which allow positional and orientational movement of aninput handle226 relative to the structure of workstation200 (seeFIG. 1A). Handle226 will generally move with a plurality of degrees of freedom relative to the workstation structure, theexemplary input device220 providing six degrees of freedom for movement ofhandle226. The linkage supporting the handle may include more or less than six degrees of freedom.
• FIG. 2A illustrateswrist224 and handle226 in more detail.Wrist224 generally comprises a gimbalassembly supporting handle226, with the handle having first andsecond grip members30a,30b.Wrist224 generally accommodates changes in orientation ofhandle226 with three orientational degrees of freedom.
• In the exemplary embodiment,wrist224 includeslinks32a,32b, and32c.Wrist224 is mounted to input arm or linkage222 (seeFIG. 2). The links of the wrist can rotate aboutaxes34a,34b,34c, and34d. Hence,wrist224 provides four orientational degrees of freedom, including one redundant orientational degree of freedom. A drive system is coupled to the wrist links so as to take advantage of this redundant degree of freedom and provide a wide range of motion as described in U.S. Pat. No. 6,714,839 entitled “Master Having Redundant Degrees of Freedom”, the full disclosure of which is incorporated herein by reference.
• Unlike the joints ofwrist224 andinput linkage222,grip members30aand30bofhandle226 pivot passively about an axis36 with no drive motor provided for feedback from the slave. In the exemplary embodiment, a hall effect transducer is mounted in one of the grip members and a magnet is mounted in the other, so that handle30 generates a grip signal indicating the angular separation betweengrip numbers30aand30b. A biasing system urges the grip members apart, and the grip members may include loops of Velcro™ or the like to more firmly position the grip members relative to a thumb and finger of the system operator. A wide variety of grip member structures might be used within the scope of the invention, including any surgical instrument handles, optionally including rigid or flexible loops for the thumb and/or fingers.
• Referring now toFIG. 3,surgical instrument14 generally includes asurgical end effector50 supported relative to ahousing53 by an elongate shaft14.1.End effector50 may be supported relative to the shaft by a distal joint or wrist so as to facilitate orienting the end effector within an internal surgical workspace.Proximal housing53 will typically be adapted to be supported by a holder of a robot arm.
• As described in more detail in U.S. Pat. No. 6,331,181, the full disclosure of which is incorporated herein by reference,instrument14 will often include amemory230, with the memory typically being electrically coupled to a data interface of aholder engaging surface232 ofhousing53. This allows data communication betweenmemory230 and a roboticsurgical processor210 of workstation200 (seeFIG. 1A). In the exemplary embodiment,memory230 comprises a Dallas chip sold with part number DS2505 having 69 kilobits of data storage capacity.
• Referring now toFIGS. 3A-3F, a variety of alternative robotic surgical tools of differing types and havingdiffering end effectors50 may be provided. Several of these end effectors, including DeBakey forceps56i, microforceps56ii, Potts scissors56iii, and clip plier56ivinclude first and secondend effector elements56a,56bwhich pivot relative to each other so as to define a pair of end effector jaws. Other end effectors, includingscalpel56vand electrocautery probe56vihave a single end effector element.
• While the present invention may find applications with surgical robotic end effectors having a single element, the invention is particularly advantageous for use with end effectors defined by multiple end effector elements. In many embodiments, the tool or end effector type can be recognized by the system through reading of some or all of the data stored bymemory230 mounted on tool14 (seeFIG. 3).
• Information from the memory can be used to perform a number of functions when the tool is loaded on the tool holder of the manipulator arm. For example, the memory can be used to provide a signal verifying that the tool is compatible with the robotic system. The tool memory may store data identifying the tool type to the robotic system so that the robotic system can reconfigure its programming to take full advantage of the tool's specialized capabilities. The tool memory can also store a specific or unique identifier for that particular tool for use in controlling tool life and hence reliability, for determining whether calibration of that particular tool has already been performed during the current (or in some embodiments, a prior) procedure, and the like. Exemplary surgical robotic tool/manipulator interface structures and details regarding data transfer between tools and robotic system processors are more fully described in U.S. Pat. No. 6,331,181 and in an application entitled, “Tool Memory Based Software Upgrades for Robotic Surgery” (Atty. Docket No. 017516-011000US), filed concurrently herewith.
• As can be understood by reference toFIGS. 1A, 1B, and4,processor210 ofworkstation200 may be configured to effect corresponding movement of a surgical instrument mounted to a robotic arm in response to movement of an input handle by employing software embodying a control logic212. Control logic212 effects movement ofend effector50 within an internal surgical site by pivoting an instrument shaft14.1 about a minimally invasive insertion point (seeFIG. 3). The control logic212 employed byprocessor210 generates motor drive signals in response to an input handle movement. These motor drive signals are transmitted to the robot arms, and cause movement at the end effector that corresponds to movement at the input handle. Logic212 ofprocessor210 can accommodate a wide variety of differing tool kinematics of a variety of differing tools (such as those illustrated inFIGS. 3A-3F) when information regarding the tool type currently mounted to a robotic arm is made available to the processor.
• Maintaining precise control over movement of surgical tools in general, and robotic surgical tools in particular, enhances the safety and therapeutic benefits of surgery. The use of elongate, relatively thin surgical instruments also enhances the benefits of robotic surgery, as such thin-shafted instruments can be inserted to an internal surgical site with less trauma to the patient. The surgical instruments, however, can be fairly sophisticated and complex mechanical assemblies, particularly where a plurality of end effector elements and/or degrees of freedom are provided at the distal end of the elongate shaft.Instruments14 may include drive systems comprising cables, pulleys, rods, gears, and the like, and these mechanical components are subject to both manufacturing tolerances and wear during the life of the tool. Additionally, the manipulator or robotic arm on which the tool is mounted may have a drive system for both transmitting motion to the tool and for moving the tool holder in space, along with having motors and position sensors for receiving drive signals from and transmitting feedback signals to the processor of the robotic system. Many of these components are also subject to deterioration from wear, along with having an initial resolution or tolerance when new. Lastly, coupling of the instrument to the robotic arm via the holder will often comprise a mechanical engagement so as to transmit mechanical movement from the motor and drive system of the robotic arm to the end effector, along with structural engagement between the housing of the instrument and the holder itself. Hence, misalignment between the end effector and an input device may have a number of sources, and may vary significantly between different robotic arms and tools mounted on robotic arm combinations.
• Telesurgical and other telerobotic systems can accommodate a certain amount of misalignment between an input device and an end effector, as described more fully in U.S. Pat. No. 6,424,885, the full disclosure of which is incorporated herein by reference. However, misalignment between the gripping members of a handle and the end effector elements of a pair of jaws can be particularly problematic.
• Referring now toFIG. 6A, a simplified reciprocal master/slave arrangement is used to illustrate actuation ofmanipulator10 so as to provide orientation and positioning ofend effector50 in response to movement ofhandle226 of theinput controller200. It should be understood that the various master and slave positions θ may comprise vectors (in Cartesian space, polar space, joint space, or the like) as well as simple angles or linear separations, and the kinematic chains of the master and slave may be quite different, often even having different degrees of freedom. To provide force feedback to the operator, the master input device is actively driven by its motors toward alignment with the position occupied byslave10. The amount of following force applied by the operator on the slave (and the reciprocal feedback on the operator's hand) are a function of a misalignment between a position (and orientation) of the master input device and apposition (and orientation) of the slave end effector.
• As illustrated schematically inFIG. 6A,master input device200 defines an actual master position θ_m^a. This actual position of the master is fed into the slave portion of the controller as a desired slave position θ_s^d. The amount of force applied by the end effectors of the slave will vary with the difference between the desired position of the slave θ_s^dand the actual position of the slave θ_m^a, with the following force on the end effectors increasing with increasing misalignment between the actual and desired positions, often with a proportional relationship.
• To provide force feedback to the operator manipulating themaster input device200, the actual slave position θ_m^ais fed back into the motors of the input device as a desired master position θ_s^d. Once again, the amount of force imposed by the motors of the master on the operator through the input device will vary with the misalignment or positional separation between the desired master position and the actual master position. This allows the operator to apply varying amounts of force through the servomechanism using the end effectors, and to have tactile feedback regarding the amount of force that has been applied.
• While the reciprocal master/slave arrangement ofFIG. 6A may be implemented to actuateend effector50 in response to manipulation ofhandle226 for gripping of objects betweenend effector elements56aand56b, the uniform following forces provided by this arrangement can have disadvantages, as can be understood with reference toFIGS. 5A-5D.End effector50 is first shown engaging a relatively large tissue T1 with no gripping force. The master position θ_mis equal to the slave position θ_s. As there is no difference between the signals generated to measure these positions, the positional error signal, separation misalignment, and following forces are all zero.
• Referring now toFIG. 5B, as the operator imposes squeezing forces onhandle226 to bring grippingmembers30a,30bcloser together (and thereby reducing the separation angle), the servomechanism begins to apply the following forces againstend effector50. As the difference between the grip angle and end effector angle increases, the following forces imposed by the end effector elements against the large tissue T1 (and the reactive forces of the tissue against the end effector) increase. Eventually, the following forces reach a maximum F_m, which may be determined by a strength of the surgical tool, a limitation of the motor torque, or a limitation based on the intended uses of the tool (for example, to avoid severing of tissues with forceps). Regardless, the servomechanism will preferably limit the following forces before irreparable damage is inflicted on the robotic system.
• To implement maximum following forces F_m, the operator has squeezed grippingmembers30a,30bwell beyond the separation angle between the end effector elements. While it is generally preferable to maintain a one-to-one correlation between the angles of the gripping members and end effector elements, having a significant misalignment to effect the maximum following forces is generally acceptable when the separation angle of the gripping members remains significantly above zero once the maximum following force F_mis imposed. Optionally, handle30 may impose reciprocal forces F_ragainst the hand of the operator to provide a tactile indication of the strength with which thick tissue T1 is being gripped to the operator.
• As illustrated inFIGS. 5C and 5D, the situation is less acceptable when a thin tissue T2 of negligible thickness is gripped. When just engaging the tissue with the elements ofend effector50, the gripping members ofhandle226 again define a separation angle that is substantially equal to the separation angle defined by the end effector elements. However, as this gripping configuration provides a quite small angular separation between the gripping members, imposition of maximum following forces F_magainst small tissue T2 only results when the gripping members are pushed beyond each other to define a negative gripping angle. This unnatural gripping actuation detracts from the operator's ability to accurately control the end effectors, particularly during delicate telepresence procedures involving the gripping of small objects, such as sutures, needles, and small tissues during telesurgery.
• Referring now toFIG. 6B, an alternative servomechanism arrangement artificially alters the actual master position θ_m^a, according to a function f to derive a desired slave position θ_s^d. Function f takes the form θ_s^d=f (θ_m^a), and is preferably an invertible (monotonic) and continuous function of the actual master position. Function g represents reciprocal forces imposed on the hand of the system operator, and will preferably also comprise a continuous, invertible function. Preferably g will provide one-to-one actuation when open, will have the slave just closed when the master is just closed, and will have a slope below the “just closed” point so that the restoring force applied against the operator's hand matches that of a conventional tool, thereby providing feedback to the operator accurately reflecting the enhanced forces provided when the end effector and handle are near their closed configurations.
• As can be understood with reference toFIGS. 6B and 5D, function f may be tailored so that once the separation between the gripping members drops below a predetermined point a small additional decrease in gripping member separation θ_m^awill result in a significantly larger change in the desired position of the slave θ_s^d. Above the predetermined point, the actual master position and desired slave position can remain the same, thereby providing the greatest dexterity for the system operator's control over the end effector.
• Referring now toFIG. 6C, an alternative servomechanism arrangement makes use of function f to alter the actual position of the grip members so as to generate the desired position of the slave end effector, as described above. However, rather than relying on a reciprocal master/slave arrangement to provide feedback of the augmented end effector forces as the grip members and end effector elements approach their closed configuration, the system ofFIG. 5C relies on abiasing system60 which interacts with the operator'shand62 to provide tactile feedback to the operator with a feed forward system, as can be understood with reference to U.S. Pat. No. 6,594,552, the full disclosure of which is incorporated herein by reference.
• As can be understood with reference toFIG. 7, a biasing mechanism such as a spring, magnet, resilient bumper, or the like can define a predetermined transition point or nominally closed position of the input handle. In the exemplary embodiment, a biasing system includes anelastomeric bushing60asurrounding agrip return spring60b. The grip return spring opens the gripping members ofhandle226 throughout their range, while the bushing provides tactile feedback to a hand of an operator when the handle reaches a nominal closed position. Continued movement of the gripping members is possible beyond the nominal closed position so as to apply force at the end effector elements. Torques are applied to endeffector elements56a,56band positions of the end effector elements are measured via adrive system70, as described more fully in the '555 patent.
• Referring now toFIG. 8, a roboticsurgical system400 includes aprocessor402 coupling first andsecond input devices404 to associatedrobotic manipulators406. Each manipulator includes atool holder408 that both holds and provides a data interface with amounted tool410. As tools will often be removed and replaced repeatedly during a surgical procedure, for example, to allow use of an electrocautery paddle followed by a needle grasper, a plurality ofalternative tools412 are available to be used in place of either of the mounted tools.
• When one type of tool is removed fromholder408 and replaced by another type of tool, data from tool memory230 (seeFIG. 3) is transmitted from the newly mounted tool to theprocessor402. This allows the processor to be reconfigured so as to allow the surgeon to accurately and safely use tools of different types. This data may also include a specific tool identifier so as to allow the processor to determine or monitor characteristics and use of that particular tool, including tool life, etc. As explained in more detail in an application entitled “Tool Memory-Based Software Upgrades for Robotic Surgery,” (Atty. Docket No. 017516-011000US), filed concurrently herewith and incorporated herein by reference, the tool memory may also be used to update data and/or software stored in a memory ofprocessor402, thereby allowing the use of new tools which have been developed, approved, and/or distributed a most recent software revision has been downloaded toprocessor402 using conventional storage media, network connections, or the like. The grip calibration procedure described herein may take place at least in part during downloading of data from mountedtool410 so as to avoid unnecessary delays in a procedure, and need not be implemented ifprocessor402 determines it is not needed, for example, if a tool type identifier stored in a memory of the tool and transmitted from the slave indicates that the mounted tool has only a single end effector or if the desired grip calibration data is already stored in a grip calibration table405 in a memory of the processor.
• For the present invention,processor402 may determine whether a particular tool has been loaded on a specific manipulator, and may store grip calibration data for that tool/manipulator combination in grip calibration table405. That grip calibration data may optionally be used if the same tool is remounted on the same manipulator. Such re-use of grip calibration data may be limited, so that the data will only be used if the tool is remounted within a time span, during a surgical procedure, a number or amount of tool use, or prior to some event.
• Manipulator406 often transmits a signal toprocessor402 indicating that a tool has been mounted toholder408.Processor402 includes agrip calibration module403, which may include hardware, software, and/or a combination of both, the grip calibration module often comprising machine readable code embodying programming instructions for implementing a grip calibration method, optionally in response to the tool-mounting signal. Using this grip calibration method,processor402 can determine and store an end effector/manipulator grip offset, which can include offsets of the instrument (due to cable stretch, manufacturing offsets, and the like), offsets of the manipulator406 (including homing error, calibration, cable stretch, and the like), and/or interface offsets resulting from the combination of tool interface232 (seeFIG. 3) withholder408. Hence, the grip calibration module ofprocessor402 can compensate for these offsets so as to improve following of end effector jaws in response to grasping of ahandle404. By adjustingprocessor402 so as to compensate for aging of the manipulator and/or end effector, the grip calibration module may maintain or improve performance of used instruments.
• Referring now toFIGS. 8, 9, and10, after instrument mounting,processor402 implements the grip calibration method. A tool type identifier and a specific tool identifier may be transmitted by the manipulator from the memory of the tool to the processor, allowing the processor to determine whether grip calibration is appropriate. For example, the processor may look-up a parameter in a table of the processor memory associated with the tool type identifier, so that tools having single end-effector elements do not undergo a grip calibration, or so that a clip applier (as illustrated inFIG. 3D) does not deploy a clip during calibration. Alternatively, the processor may determine from the tool identifier that the mounted tool has previously been mounted to the same manipulator previously during the same procedure, and may therefore look-up the desired calibration information from a calibration data table405. The calibration data table my comprise jaw closure offset for specific tool manipulator combinations.
• Ifprocessor402 determines that a new calibration procedure is appropriate for the mounted tool, the processor transmits drive signals tomanipulator408 on which atool410 has been mounted. In response to these signals, one or more motors ofmanipulator406 move the end effectors into mutual engagement, with the motors typically applying torque to the end effectors via a coupling drive system (seeFIG. 12) so as to attempt to move even further against each other, thereby squeezing the end effector closed. In the exemplary embodiment, the processor may command a trajectory or movement of the end effector, causing a servo controller loop of the processor to calculate a commanded motor torque using a position of the end effector element.Processor402 monitors and stores joint position and commanded torque data as illustrated inFIGS. 9 and 10, respectively. The servo counts shown inFIGS. 9-12C can represent time, with the exemplary servo loop operating with a cycle frequency of 1333 Hz.
• When the end effector elements are commanded to move from an open configuration to beyond a closed configuration, a significant change in commanded torque may be expected where the end effector are first fully closed, which may be referred to as a mutual engagement configuration. In other words, the associated motor will be driven harder to effect the commanded movement after the end effectors begin pushing against each other. This change in commanded torque may appear as a “knee” in the commanded torque graph ofFIG. 10. However, the precise location of the knee may not be immediately clear. To facilitate identification of the end effector mutual engagement position, it is helpful to limit the analysis of the data to a limited range. The data may be restricted to a position range within which engagement is expected to occur, thereby assuming that the calibration offset will be within a predetermined range. For example, it may be assumed that the calibration offset for the end effector mutual engagement configuration will be between a nominal or initially commanded configuration of the jaws being open by 5 degrees (+5 degrees), and the jaws being squeezed past closed by 20 degrees (−20 degrees).
• The commanded torque plot ofFIG. 10 may reflect variations in torque applied to compensate for friction in the manipulator, to enhance precision, and the like, as more fully described in U.S. Pat. No. 6,565,554. These commanded torques are effectively noise when determining grip calibration, with the noise primarily being at approximately the Nyquiest frequency, largely above the frequency of interest for calibration analysis. Hence, it may be helpful to include in processor402 a filter to help identify the knee in the commanded torque draft. The filter may comprise a low pass filter, the exemplary filter comprising a 5 Hz low pass Butterworth filter, although other frequencies might also be used. The filtered commanded torque in the area of interest is illustrated inFIG. 11, showing the expected knee.
• Referring now toFIGS. 11 and 12A-12C, the mutual engagement configuration of the end effector should correlate with the position of greatest curvature in the negative direction of the commanded torque data. This can be identified from the minima of the second derivative of the commanded torque. Once the mutual engagement configuration is known, calibration of the mounted tool can then be effected by applying a difference between the actual position and the commanded position of the end effectors as an offset to the grip controllers described above, for example, so that the closed configuration of the handle226 (at which the handle members first engage theresilient bumper60a) corresponds to the mutual engagement configuration of the end effectors. This difference can be stored as an offset in grip calibration data table405 for the tool/manipulator combination.
• Typically, grip calibration will take over a half a second to implement, often taking over a second, with the exemplary embodiment taking about 2 seconds. To avoid excessive delays during a procedure,processor402 may store the grip calibration offset or other grip data in a memory of the processor, with the memory ideally storing a table of grip calibrations and instrument identifiers for each manipulator, so that the processor records each end effector/manipulator combination used during a surgical procedure. If an instrument has already been used during a procedure, the stored calibration may be used without repeating the grip calibration—if the mounted instrument has not previously been mounted on that particular manipulator during a procedure, the grip calibration will be performed. Grip calibration may be performed during data reading from and/or writing to information on the memory of the tool, which may occur when a tool is first used in each procedure.
• Grip calibration may not determine an appropriate offset for a tool/manipulator combination for a variety of reasons, including a broken cable or failure of the tool interface to properly engage with the tool holder, a tool never reaching the commanded or mutual engagement configuration, and the like. For calibration failures, the grip calibration offset can be safely set to zero, so that the tool is assumed to be at the nominally commanded configuration, as the instruments may be inoperative (and hence will not be used anyway). By not storing data for calibration failures, the processor may treat the tool as not previously having been mounted on the manipulator, so that calibration can again be attempted.
• Optionally, the grip calibration procedure may be deemed inappropriate for one or more tool types having two end effector elements. For example, although a clip applier as illustrated inFIG. 3D may benefit a grip calibration, such a calibration may actuate a clip prior to the clip reaching the target tissue. Hence, the processor may forego grip calibration in response to some tool type identifiers of such tools.
• While the exemplary embodiments have been described in detail, for clarity of understanding and by way of example, a variety of changes, adaptations, and modifications will be obvious to those of skill in the art. Hence, the scope of the present invention is limited solely by the appended claims.

Claims (13)

1-23. (canceled)

24. A method for calibrating a robotic end effector, the end effector comprising first and second end effector members, the method comprising:

applying a torque to at least one of the end effector members to move the first end effector member closer to the second end effector member;

monitoring the applied torque;

monitoring the position of the first end effector member relative to the second end effector member versus the monitored applied torque;

determining a position corresponding to mutual engagement of the first and second end effector members; and

storing said position corresponding to mutual engagement in a memory.

25. The method ofclaim 24, the determining a position corresponding to mutual engagement comprising determining a position corresponding to a relative increase in the absolute curvature of the monitored applied torque versus the position.

26. The method ofclaim 25, the determining a position corresponding to a relative increase in the absolute curvature being performed over a range of positions less than the full range of positions over which the end effector members may be maneuvered.

27. The method ofclaim 25, the determining a position corresponding to a relative increase in the absolute curvature comprising determining a position corresponding to a relative increase in the absolute value of the second derivative of the monitored applied torque versus the position.

28. The method ofclaim 24, further comprising, during normal operation:

adjusting the position of a first grip relative to a second grip in a grip controller;

adjusting the position of the first end effector member relative to the second end effector member in response to the adjusting the position of the first grip relative to the second grip by applying a torque to at least one of the first and second end effector members;

applying an offset between the adjusted position of the grip controller versus the adjusted position of the end effector, the offset corresponding to the stored position corresponding to mutual engagement.

29. The method ofclaim 24, wherein the monitored applied torque is filtered by a low-pass filter before the determining the position corresponding to mutual engagement.

30. The method ofclaim 24, the applied torque monitored over a limited position range.

31. The method ofclaim 24, further applied to calibrate a second robotic end effector, the results of the calibrating the first and second robotic end effectors stored in a memory.

32. A system for calibrating a robotic end effector, the end effector comprising first and second end effector members, the system comprising:

means for applying a torque to at least one of the end effector members to move the first end effector member closer to the second end effector member;

means for monitoring the applied torque;

means for monitoring the position of the first end effector member relative to the second end effector member versus the monitored applied torque;

means for determining a position corresponding to mutual engagement of the first and second end effector members; and

means for storing said position corresponding to mutual engagement in a memory.

33. The system ofclaim 32, further comprising:

a grip controller comprising a first grip and a second grip;

means for adjusting the position of the first end effector member relative to the second end effector member in response to the adjusting the position of the first grip relative to the second grip by applying a torque to at least one of the first and second end effector members; and

means for applying an offset between the adjusted position of the grip controller versus the adjusted position of the end effector, the offset corresponding to the stored position corresponding to mutual engagement.

34. A computer program product for calibrating a robotic end effector, the product comprising computer-readable medium comprising:

code for causing a computer to apply a torque to at least one of the end effector members to move the first end effector member closer to the second end effector member;

code for causing a computer to monitor the applied torque;

code for causing a computer to monitor the position of the first end effector member relative to the second end effector member versus the monitored applied torque;

code for causing a computer to determine a position corresponding to mutual engagement of the first and second end effector members; and

code for causing a computer to store said position corresponding to mutual engagement in a memory.

35. The computer program product ofclaim 34, further comprising:

code for causing a computer to adjust the position of a first grip relative to a second grip in a grip controller;

code for causing a computer to adjust the position of the first end effector member relative to the second end effector member in response to adjusting the position of a first grip relative to a second grip in the grip controller; and

code for causing a computer to apply an offset between the adjusted position of the grip controller versus the adjusted position of the end effector, the offset corresponding to the stored position corresponding to mutual engagement.

Images